Three-dimensional printing, also known as additive manufacturing, is a process of making a three-dimensional solid object from a digital model of virtually any shape. Many three-dimensional printing technologies use an additive process in which an additive manufacturing device forms successive layers of the part on top of previously deposited layers. Some of these technologies use extruders that soften or melt extrusion material, such as ABS plastic, into thermoplastic material and then emit the thermoplastic material in a predetermined pattern. The printer typically operates the extruder to form successive layers of the thermoplastic material that form a three-dimensional printed object with a variety of shapes and structures. After each layer of the three-dimensional printed object is formed, the thermoplastic material cools and hardens to bond the layer to an underlying layer of the three-dimensional printed object. This additive manufacturing method is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
Many extruders are fed extrusion material filaments that are melted or softened to form the thermoplastic material. Even though the filaments are produced in a full range of colors, current extruders in three-dimensional object printers have very limited color capability. Typically, extruded materials of different colors are produced with separate extruders that extrude material of only one color. Because the extruded thermoplastic material possesses high viscosity, the different extruded materials are difficult to mix. Therefore, most printers of this type are limited to two differently colored materials. The differently colored materials from two separate extruders can be used to make a color image in or on an object by printing a base of the object in one color and a pattern in the second color on top of the base. Adding multiple extruders to a printer adds greatly to the complexity of the printer, but only provides a limited color range. Making an outline of an object with extruded thermoplastic materials from multiple extruders invariably leaves breaks in the surface. To avoid these breaks, different colors are alternated from one layer to another.
Another printer configuration used to produce differently colored extruded materials uses a filament splicer that produces a single multi-color filament from a plurality of differently colored extrusion material filaments by combining them serially lengthwise. The single multi-color filament is fed to a heater that feeds a single extruder. Thus, the thermoplastic material extruded by the extruder changes as the differently colored sections of the filament are melted or softened. The splicer pre-calculates the amount of a thermoplastic material required to form a portion of the object having a particular color and a segment of an extrusion material filament of that color is spliced into the single filament. By continuing to splice an appropriate length of a filament of another color to the single filament, the extruder can continue to produce the object until its formation is complete. This splicer is primarily used to form areas of solid color in the object. The use of the splicer requires precise calculations regarding the lengths of the different filament segments to form the single filament and limits the resolution of the thermoplastic materials extruded by the extruder. Additionally, detecting whether the delivery of the thermoplastic material produced from the multi-colored filament is synchronized with the formation of the appropriate object portions is difficult.
Providing a three-dimensional object printer with a greater range of colors over known printers and enabling a variety of techniques for forming the object would be beneficial.